The reliability of telecommunication systems that users have come to expect and depend on is based, in part, on the systems' reliance on redundant equipment and power supplies. Telecommunication switching systems, for example, route tens of thousands of calls per second. The failure of such systems, due to, for instance, the loss of incoming AC power, may result in a loss of millions of telephone calls and a corresponding loss of revenue.
Power plants, such as battery plants, attempt to alleviate the power loss problem by providing the telecommunication system with a backup power supply for use in the event that the incoming AC power is interrupted. Since the backup power supply is often called upon to provide power to the load for durations longer than just a few seconds, the implementation of a battery backup system has a significant impact on both the performance and the cost of the power plant.
A concern with respect to battery plants is managing the transition from a normal or primary mode of operation to a backup mode of operation requiring the use of a backup power system. A control circuit used to manage such a transition is required to detect when there is an absence of primary power to a primary power system and switch to the backup power system. Typically, the primary power system and the backup power system are voltage sources having a low output impedance. Since the outputs of the low output impedance voltage sources cannot generally be directly coupled together without causing serious circulating current problems (resulting in probable component damage), the transition must be orchestrated carefully. This requirement typically increases the complexity and therefore the cost of such control circuits.
Another perhaps more strategic concern is the ability of the power system to continue to operate when a component or collection of components experience a fault. Present fault-tolerant structures often depend on a multiplicity of completely redundant circuits or systems wherein one or more of such circuits or systems may be completely removed from the system if they become faulted. This approach, of course, increases the overall cost proportionally and may raise the overall reliability only marginally depending on a particular configuration.
Accordingly, what is needed in the art is a dual input power supply and a method of operating the power supply that overcomes the deficiencies of the prior art.